Optical connector

ABSTRACT

An optical fiber connector plug includes a housing through which extends a cable containing at least one optical fiber. A ferrule, which is supported by the housing, is provided for receiving the optical fiber. The ferrule has a mating facet and an opposing rear facet located in the housing. The ferrule has at least one guide pin thru-hole and at least one optical fiber thru-hole extending between the mating facet and the opposing rear facet. The guide pin thru-hole has an opening portion extending inward from the mating facet. The opening portion is tapered outward to meet the mating facet in an oblique manner such that the opening portion has a diameter in the plane of the mating facet that is greater than a diameter of a remainder of the guide pin thru-hole.

FIELD OF THE INVENTION

The present invention relates generally to optical fiber connectors andmore particularly to a multifiber optical connector.

BACKGROUND OF THE INVENTION

Optical fibers are being increasingly utilized for a variety ofapplications such as data transmission. In order to interconnect theoptical fibers, fiber optic connectors are typically mounted upon theend portions of the optical fibers that are to be mated. The opticalconnections established by mating a pair of fiber optic connectorspreferably have relatively low attenuation and a small return loss. Inthis way such connectors permit the implementation of data transmissionat high bandwidths and high transmission capacities over relatively longdistances. Moreover, the increasing demand for high transmissioncapacities leads to optical fibers that are laid in parallel, which inturn require multifiber connectors.

A variety of standardized optical fiber connectors have been developedwhich are widely used in the industry to interconnect the optical fibersemployed in transmission systems. One known type of fiber opticconnector is a so-called “MT” type. The MT connector has a connectorhousing with a front end and a ferrule movably mounted in the housing.The ferrule is biased by a spring to a forward position. When theferrule is in the forward position, a front face of the ferrule projectsfrom the housing. A multi-fiber cable extends into the housing. Theindividual fibers of the cable extend through the ferrule to the frontface. The front face of the ferrule, and the ends of the fibers, arepolished to form a flat surface. The fiber ends are precisely locatedwithin the ferrule. The ferrule also has pin-receiving bores. A maleMT-type connector has guide pins located in the bores, which projectbeyond the front face of the ferrule. In a female MT connector the boresremain empty. Two cables may be connected to one another by engagingmale and female MT connectors with one another so that the guide pins ofthe male connector enter the pin receiving bores of the femaleconnector.

While these connectors can provide a good connection between theindividual fibers of the two cables with low optical transmissionlosses, some modern applications are placing increased performance andreliability demands on them. In particular, the connectors must meetTelcordia GR-1435-CORE requirements. For example, Telcordia requirementsspecify that optical fiber connectors have an insertion loss that doesnot exceed 0.80 dB. The connector should continue to meet thisrequirement after being mated and remated 200 times without cleaningafter every mating (only cleaning after 25 mates is permitted on oneside of the connector and after 50 mates for the other side). Therequirement is intended to ensure that the connector does not selfgenerate contamination that may inhibit its performance. Unfortunately,conventional multifiber optical connectors generally do not satisfy thisrequirement unless the connector is thoroughly cleaned more frequentlythan the Telcordia requirements.

This insertion loss degradation is particularly problematic when theseconnectors are employed in optical backplanes. When used in opticalbackplanes the contaminated connector surfaces are often located withinother equipment to which it can be difficult to gain access to clean thecontamination from the connector.

SUMMARY OF THE INVENTION

In accordance with the present invention, an optical fiber connectorplug includes a housing through which extends a cable containing atleast one optical fiber. A ferrule, which is supported by the housing,is provided for receiving the optical fiber. The ferrule has a matingfacet and an opposing rear facet located in the housing. The ferrule hasat least one guide pin thru-hole and at least one optical fiberthru-hole extending between the mating facet and the opposing rearfacet. The guide pin thru-hole has an opening portion extending inwardfrom the mating facet. The opening portion is tapered outward to meetthe mating facet in an oblique manner such that the opening portion hasa diameter in the plane of the mating facet that is greater than adiameter of a remainder of the guide pin thru-hole.

In accordance with one aspect of the invention, the tapered openingportion is defined by curved sidewalls.

In accordance with another aspect of the invention, the tapered openingportion is defined by flat sidewalls.

In accordance with another aspect of the invention, the flat sidewallsform a 45° angle with respect to the mating facet.

In accordance with another aspect of the invention, the mating facet ofthe ferrule defines an oblique surface with respect to a longitudinalaxis of the thru-holes.

In accordance with yet another aspect of the invention, a multifiberoptical fiber connector is provided. The connector includes a firstconnector plug that has a first housing through which extends a cablecontaining at least one optical fiber. A first ferrule, which issupported by the housing, is provided to receive the optical fiber. Theferrule has a mating facet and an opposing rear facet located in thehousing. The first ferrule has at least one guide pin thru-hole and atleast one optical fiber thru-hole extending between the mating facet andthe opposing rear facet. The guide pin thru-hole has an opening portionextending inward from the mating facet. The opening portion is taperedto meet the mating facet in an oblique manner such that the openingportion has a diameter in the plane of the mating facet that is greaterthan a diameter of a remainder of the guide pin thru-hole. The connectoralso includes a second connector plug for mating with the firstconnector plug. The second connector plug has a second housing throughwhich extends a cable containing at least one optical fiber. A secondferrule, which is supported by the second housing, is provided toreceive a second plurality of optical fibers. The ferrule has a matingfacet and an opposing rear facet located in the housing. The ferrule hasat least one guide pin receptacle and at least one optical fiberthru-hole extending between the mating facet and the opposing rearfacet. A guide pin is secured in the guide pin receptacle.

In accordance with another aspect of the invention, the guide pin has anend portion distal from the second ferrule. The end portion has afrustoconical shape. Alternatively, the end portion may be smoothlytapered.

In accordance with another aspect of the invention, a guide pin holdingmember is provided for supporting the guide pin in the guide pinreceptacle.

In accordance with another aspect of the invention, an engagement memberis provided for connecting the first and second housings together sothat the guide pin extending from the second ferrule is secured in theguide pin thru-hole in the first ferrule.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a multifiber optical connector plug assembly in which thepresent invention may be employed.

FIG. 2 shows an exploded view of the multifiber optical connector plugassembly depicted in FIG. 1.

FIG. 3 shows a multifiber optical connector formed from two of themultifiber optical connector plug assemblies depicted in FIGS. 1 and 2.

FIG. 4 shows a conventional guide pin.

FIG. 5 shows a fragmentary, cross-sectional view of a ferruleillustrating a conventional guide pin insertion hole.

FIG. 6 shows a fragmentary, cross-sectional view of one embodiment ofthe ferrule constructed in accordance with the present invention.

FIG. 7 shows a fragmentary, cross-sectional view of an alternativeembodiment of the ferrule constructed in accordance with the presentinvention.

FIG. 8 shows a guide pin constructed in accordance with the presentinvention.

FIG. 9 shows a functional block diagram of an exemplary WDM ring networkin which the one or more of the connectors of the present invention maybe employed.

DETAILED DESCRIPTION

One embodiment of a multifiber optical connector plug assembly in whichthe present invention may be employed is shown in FIG. 1 and FIG. 2.While the features of the present invention will be illustrated inconnection with a particular MT-type connector, those of ordinary skillin the art will recognize that the invention can be applied to manyother optical fiber connectors. Other connector types in which thepresent invention may be employed include, without limitation, MPX, MPO,MTP, HBMT, SMC and OGI connectors.

The multifiber optical connector plug assembly includes a multifiberconnector ferrule 103A housing a plurality of transversely arrangedoptical fibers 102 projecting out of the end of an optical fiber ribbon101 and having a pair of guide pin insertion holes 104 with thetransversely arranged optical fibers 102 located therebetween. Aconnecting facet 105 of the ferrule 103A has a flat surface nearlyperpendicular to the optical axes of the optical fibers 102. A guide pinholding member 130 is provided behind the multifiber connector ferrule103A for holding the guide pins inserted into the guide pin insertionholes 104 and to prevent the guide pins (when present) from extendingbehind the multifiber connector ferrule 103A. A spring member 126 isprovided behind the guide pin holding member 130 for pressing themultifiber connector ferrule 103A against a mated multifiber connectorferrule in an axial direction. A front housing 127 and a rear housing128 integrally house the multifiber connector ferrule 103A, the guidepin holding member 130, and the spring member 126 together.

As shown in FIG. 2, the guide pin holding member 130 has guide pinholding holes 131 having inner diameters slightly smaller than those ofthe guide pins, and slits 132 for splitting the upper parts of thecircumferences of the guide pin holding holes 131. When the guide pins(not shown in FIG. 2) are inserted into the guide pin insertion holes104 and reached the guide pin holding member 130 located behind themultifiber connector ferrule 103A, the slits 132 are elasticallydeformed by the thrusting guide pins 106 to widen the guide pin holdingholes 131 such that the tip ends of the guide pins 106 can be insertedinto and held inside the guide pin holding holes 131.

As shown in FIG. 3, in connecting two multifiber optical connector plugassemblies to form a multifiber optical connector, a male multifiberoptical connector plug assembly A is inserted into one opening of anadaptor B until hook members 30 provided on the adaptor B are engagedwith groove portions 29 formed on the front housing 27 of the multifiberoptical connector plug assembly A.

Then, a female multifiber optical connector plug assembly A′ is insertedinto another opening of the adaptor B until the hook members 30′provided on the adaptor B are engaged with groove portions 29′ formed onthe front housing 27′ of multifiber optical connector plug assembly A′.The guide pins 6 are inserted into the guide pin insertion holes 104′ offemale multifiber optical connector plug assembly A′, such that thealignment of the optical fibers housed inside the multifiber opticalconnector plug assemblies A and A′ is provided by guide pins 6.

In a case of reconnection or switching, the detachment of the multifiberoptical connector plug assemblies is achieved by releasing theengagement of the hook members 30 and 30′ of the adaptor B with thegroove portions 129 and 129′ of the multifiber optical connector plugassemblies A and A′, and pulling the multifiber optical connector plugassemblies A and A′ out of the adaptor B. As shown in FIG. 4, the tips40 of the guide pins 106 are generally frustoconical in shape so as todefine an angle of about 20°-40° relative to the longitudinal axis ofthe guide pin. The frustoconical shape of the guide pin tips allows foreasier insertion of the guide pin into the guide pin insertion holes104′.

The present inventors have determined that a problem with conventionferrules is that the action of mating the male connector with the femaleconnector causes the guide pin to press against the edge of theinsertion holes in the female connector, which causes small particles tobreak away from the edge of the insertion holes. The particlescontaminate the optical fiber on the male and female ferrules in theplane of the ferrule facet 105. Continued mating and decoupling of theconnectors also may cause the small particles to accumulate on or nearthe fiber core at the connector surface 105. These particles canattenuate light coupled through the fiber core by scattering,absorption, or by mechanically preventing intimate fiber-to-fibercontact of the respective connector surfaces 105. As such, theattenuation of the resulting optical connection significantly increases.

In accordance with the present invention, the sharp edges of the guidepin insertion holes in the ferrule of the female connector are removedto reduce the likelihood of small particles breaking away and to providea lead-in for the guide pins at the entrance to the insertion holes.FIG. 5 shows a fragmentary, cross-sectional view of a ferrule 50illustrating a conventional guide pin insertion hole 52. The insertionhole forms a substantially right angle with the mating facet 54 of theferrule. FIG. 6 shows a fragmentary, cross-sectional view of oneembodiment of the ferrule 60 constructed in accordance with the presentinvention. The entrance to the insertion hole 62 of ferrule 60 is curvedaway from the center of the hole so that it meets the mating facet 64 atan oblique angle. That is, the entrance to the insertion hole of theferrule is tapered outward as it approaches the mating facet 64.

FIG. 7 shows an alternative embodiment of the invention in which theentrance to the insertion hole 82 of ferrule 80 has a flat taper insteadof a curved taper as in FIG. 6. In one particular embodiment of theinvention the sidewalls of the flat taper forms a 45° angle with themating facet 84.

In some embodiments of the invention the tip of the guide pin isconfigured to eliminate the sharp edge seen in the conventional guidepin depicted in FIG. 4. Rather, as seen in FIG. 8, the tip of the guidepin has an elliptical profile to reduce the stress placed upon the edgeof the guide pin insertion hole by the guide pin.

Experiments were performed using various embodiments of the presentinvention to determine the characteristics and reliability of theconnectors. The connectors that were employed in the experiments wereconstructed to support eight single mode optical fibers that weretransversely arranged with a 0.25 mm interval between adjacent fibers.The guide pin insertion holes had curved tapered as depicted in FIG. 6.The outer diameter of each optical fiber was about 0.25 mm. The ferrule,which was formed from glass-filled epoxy, had a pair of guide pininsertion holes and eight optical fiber holes. The guide pin insertionholes were about 0.71 mm in diameter. The entrance to the insertionholes had a maximum diameter of 1.32 mm. The radius of curvature of thesidewall entrance to the guide pin insertion holes was about 0.30 mm.After the optical fibers were inserted into the insertion holes andfixed with adhesive therein, an oblique polishing process was appliedonto the mating facet of the ferrule to form an oblique surface which isinclined with respect to the optical axes of the optical fibers by anangle of 8 degrees, which is an angle that minimizes light reflectedfrom the interface of single mode optical fibers. The cross sectionalsize of the connecting facet was about 11 mm². A buffing polishingprocess was then applied onto the obtained oblique surface so that theoptical fibers extended about 0.00003 mm beyond the mating facet.

The experiment was conducted by measuring the connection loss afterrepeatedly mating and re-mating the connectors. The average lossremained below 0.30 dB even after being re-mated over 200 times.

FIG. 9 shows a functional block diagram of an exemplary WDM ring network800 in which the one or more of the connectors of the present inventionmay be employed. The connectors may be used to interconnect the variouscomponents of the network. In some cases the interconnections may beperformed via an optical backplane. The backplane provides optical pathsthrough which various optical modules are coupled. The backplane willtypically be located in a rack in which the optical modules are to belocated.

Ring network 800 includes a plurality of nodes 802-805 connected along acontinuous, or looped, optical path 810. Each of these nodes istypically linked by a segment of optical fiber. Optical amplifiers 820are located at appropriate points along the optical fiber segmentsNodes802-805 generally include an optical switch such as an opticalcrossconnect or an optical add/drop multiplexer (OADM), user interfaces,and a network management element. The optical switches may be staticswitches in which particular wavelengths received on optical path 810can only be received by predetermined ones of the local ports of thenodes. Alternatively, one or more of the optical switches may bereconfigurable optical switches in which any wavelength channel can beselectively dropped to any local port of the nodes. Such reconfigurableoptical switches may be electro-optical elements, or, more preferably,all-optical elements. Examples of an all-optical reconfigurable switchare disclosed in U.S. patent application Ser. Nos. 09/571,833 and09/691,812, which are hereby incorporated by reference in theirentirety. Of course, those of ordinary skill in the art will recognizethat the present invention is equally applicable to other networktopologies in addition to rings such as mesh or point-to-pointtopologies, for example.

1. An optical fiber connector plug, comprising: a housing through whichextends a cable containing at least one optical fiber; a ferrulesupported by said housing for receiving said at least one optical fiber,said ferrule having a mating facet and an opposing rear facet located insaid housing, said ferrule having at least one guide pin thru-hole andat least one optical fiber thru-hole extending between the mating facetand the opposing rear facet, said guide pin thru-hole having an openingportion extending inward from the mating facet, said opening portionbeing tapered outward to meet the mating facet in an oblique manner suchthat said opening portion has a diameter in the mating facet that isgreater than a diameter of a remainder of the guide pin thru-hole. 2.The optical fiber connector plug of claim 1 wherein said tapered openingportion is defined by curved sidewalls.
 3. The optical fiber connectorplug of claim 1 wherein said tapered opening portion is defined by flatsidewalls.
 4. The optical fiber connector plug of claim 3 wherein theflat sidewalls form a 45° angle with respect to the mating facet.
 5. Theoptical fiber connector plug of claim 1 wherein said at least one guidepin thru-hole comprises a plurality of guide pin thru-holes.
 6. Theoptical fiber connector plug of claim 1 wherein said at least oneoptical fiber thru-hole comprises a plurality of optical fiberthru-holes.
 7. The optical fiber connector plug of claim 5 wherein saidat least one optical fiber thru-hole comprises a plurality of opticalfiber thru-holes.
 8. The optical fiber connector plug of claim 1 whereinsaid mating facet of the ferrule defines an oblique surface with respectto a longitudinal axis of said thru-holes.
 9. The optical fiberconnector plug of claim 1 wherein said connector plug is an MT-typeconnector.
 10. The optical fiber connector plug of claim 1 wherein saidconnector plug is of a type selected from the group consisting of MPXMPO, MTP, HBMT, SMC and OGI type connectors.
 11. The optical fiberconnector plug of claim 1 wherein said ferrule is formed fromglass-filled epoxy.
 12. A multifiber optical fiber connector,comprising: a first connector plug that includes: a first housingthrough which extends a cable containing at least one optical fiber; afirst ferrule supported by said first housing for receiving said atleast one optical fiber, said ferrule having a mating facet and anopposing rear facet located in said first housing, said first ferrulehaving at least one guide pin thru-hole and at least one optical fiberthru-hole extending between the mating facet and the opposing rearfacet, said guide pin thru-hole having an opening portion extendinginward from the mating facet, said opening portion being tapered to meetthe mating facet in an oblique manner such that said opening portion hasa diameter in the mating facet that is greater than a diameter of aremainder of the guide pin thru-hole; a second connector plug for matingwith the first connector plug, said second connector plug including: asecond housing through which extends a cable containing at least oneoptical fiber; a second ferrule supported by said second housing forreceiving a second plurality of optical fibers, said ferule having amating facet and an opposing rear facet located in said second housing,said ferrule having at least one guide pin receptacle and at least oneoptical fiber thru-hole extending between the mating facet and theopposing rear facet; a guide pin secured in said guide pin receptacle.13. The multifiber optical fiber connector of claim 12 wherein saidguide pin has an end portion distal from the second ferrule, said endportion having a frustoconical shape.
 14. The multifiber optical fiberconnector of claim 12 wherein said guide pin has an end portion distalfrom the second ferrule, said end portion being smoothly tapered. 15.The multifiber optical fiber connector of claim 12 wherein said taperedopening portion of the guide pin thru-hole is defined by curvedsidewalls.
 16. The multifiber optical fiber connector of claim 12wherein said tapered opening portion of the guide pin thru-hole isdefined by flat sidewalls.
 17. The multifiber optical fiber connector ofclaim 16 wherein the flat sidewalls form a 45° angle with respect to themating facet.
 18. The multifiber optical fiber connector of claim 12wherein said at least one guide pin thru-hole comprises a plurality ofguide pin thru-holes and said at least one optical fiber thru-hole ineach of the first and second ferrules comprises a plurality of opticalfiber thru-holes.
 19. The multifiber optical fiber connector of claim 12wherein said mating facets of the first and second ferrules define anoblique surface with respect to a longitudinal axis of their respectivethru-holes.
 20. The multifiber optical fiber connector of claim 12further comprising a guide pin holding member for supporting said guidepin in said guide pin receptacle.
 21. The multifiber optical fiberconnector of claim 12 further comprising an engagement member forconnecting said first and second housings together so that said guidepin extending from the second ferrule is secured in the guide pinthru-hole in the first ferrule.
 22. The multifiber optical fiberconnector of claim 12 wherein said first and second connector plugs areMT-type connectors.
 23. The multifiber optical fiber connector of claim12 wherein said first and second connector plugs are of a type selectedfrom the group consisting of MPX, MPO, MTP, HBMT, SMC and OGI typeconnectors.
 24. The multifiber optical fiber connector of claim 12wherein said first and second ferrules are formed from glass-filledepoxy.